[TowerTalk] antenna impedance anomaly

[Al Williams]

Not too long ago, when I asked why reflectors of a Yagi are longer than the driven element and directors of a Yagi are shorter than the driven element, several Towertalkians advised me to look at the current table output.  In particular to look at the phase angle of the segments.  One respondent advised that the reason is that "....that is the way it is..."!  At first I scoffed at this response but after thinking about the difficulty of adding the current phase angle to the time delay angle caused by the separation between elements for all combination of segments, I decided that yes, that is the way it is.  What the computer can do in a fraction of a second is beyond what I could do.

However I "discovered" what seems very odd to me and am hoping that Towertalkians can  explain it.

I modeled a 40 meter dipole at 60' above medium ground using EZNEC with real/high accuracy.  At resonance the source impedance angle was reduced to zero and for frequencies above resonance the phase angle started increasing positively (inductive).  For frequencies below resonance the phase angle started increasing negatively (capacitive).  This is in agreement with what antenna books inform us.

But the phase angle of each segment (except the center one) always was negative with increasing angle as the segment chosen goes to the end of the element.
(In this case 31 segments per element).  This negative phase angle was reported for both higher and lower frequencies (equivalent to shorter and longer elements?).

Why do individual segments always show a capacitive phase angle while the whole element will show either capacitive, zero, or inductive phase angle?

k7puc